1. Field of the Invention
The invention relates to a synthetic resin made check valve provided to a pipeline somewhere therethrough in which a washing solution or a corrosive solution flows in, for example, a semiconductor manufacturing process.
2. Description of the Related Art
There are imposed high degree requirements for cleanness on a check valve provided to a pipeline somewhere therethrough for supplying a washing solution or an etching solution in a washing step or etching step during a semiconductor manufacturing process. To avoid contamination due to metal ions, especially, a check valve provided to such a pipeline somewhere therethrough is made of a synthetic resin excellent in corrosion resistance and wear resistance such as a fluororesin (e.g., PFA, PP, PE).
Conventionally, such a check valve is configured, as shown in FIG. 3 for example, in such a way that to a channel 51 passing through a PFA-made check valve main body 50 is provided a large-diameter valve disc housing chamber 52, in which are housed a spherical ball valve disc 53 and a spring 54 for pressing this ball valve disc 53 in a valve-closing direction. These ball valve disc 53 and the spring 54 are also made of a synthetic resin such as PFA.
With a check valve having the above-mentioned configuration, the channel 51 arranged on the upstream side (right side in the figure) of the valve disc housing chamber 52 is held in a valve-closed state with the ball valve disc 53 as butted by a pressing pressure of the spring 54 against a marginal open edge (valve seat) 55 open to the valve disc housing chamber 52. If, on the other hand, a fluid pressure of a fluid flowing into the above-mentioned channel 51 exceeds in strength a springing force of the spring 54, the ball valve disc 53 moves in a valve-opening direction as compressing the spring 54. With this, this ball valve disc 53 is separated from the above-mentioned valve seat 55 into a valve-opened state, thus flowing the fluid via the valve disc housing chamber 52 toward the downstream side.
The check valve with the above-mentioned configuration, however, suffers from a problem that as the springing force of the spring 54 weakens, sealing performance of the valve in its opened state with the ball valve disc 53 as butted against the valve seat 55 is gradually deteriorated. That is, the spring 54 is provided into the valve disc housing chamber 52 as having a predetermined amount of compressive deformation in order to hold the ball valve disc 53 as butted against the valve seat 55 in the valve-closed state. With this, when the valve is opened, that compressive deformation amount becomes even larger.
In this state, with the check valve of the above-mentioned configuration, the spring 54 is liable to be put into a full compressed state in response to a fluid pressure of an incoming fluid, thereby generating a large internal pressure. When used repeatedly in such a stress state, the spring 54 made of a synthetic resin is subjected to stress relaxation (creep), thus easily deteriorating from its initial springing force. This in turn reduces the pressing force in the valve-closed state, thus making it impossible to maintain sufficient check valve functions.
In view of the above, it is an object of the invention to provide a check valve that can maintain its own stable functions by suppressing deterioration in the springing force of the spring made of a synthetic resin.
With this, a check valve specified in claim 1 comprises: a check valve main body having a channel passing therethrough; a synthetic resin-made valve disc provided to the above-mentioned channel somewhere therethrough, for opening and closing this channel; a spring made of a synthetic resin for pressing this valve disc in the valve-closing direction; and valve-disc movement-amount regulating means for regulating an amount of the valve of moving in the valve-opening direction to prevent the spring from being subjected to full compression, wherein if the above-mentioned valve disc is subjected to a fluid pressure in the valve-opening direction in excess of a pressing pressure of the spring, the valve disc may be opened in the valve-opening direction with the spring as compressed, thus opening the above-mentioned channel.
With this configuration, even when a large fluid pressure is applied to the valve disc in its opening direction, the valve is regulated halfway in its movement by the valve-disc movement-amount regulating means, thus holding the spring as subjected to a compression amount lower than a full compression amount. With this, the spring can be prevented from being compressive-deformed excessively, so that it is possible to suppress deterioration due to stress relaxation in the springing force of the spring, even though it is made of a synthetic resin. As a result, deterioration can be suppressed in the pressing force of the spring onto the valve disc in its closing direction when it is returned to its closed state, thus maintaining stable check valve functions.
claim 2 features the check valve specified in claim 1, wherein spring holding means is provided for suppressing displacement of the spring in a radial direction.
With this configuration, it is possible to suppress displacement of the spring in a radial direction, to inhibit axial shift between this spring and the valve disc. As a result, deviation can be suppressed from occurring in the pressing force of the spring onto the valve disc butted against the valve seat of the check valve main body when it is closed, to maintain a uniform pressing state everywhere on a circumference, thereby providing good sealing performance in the valve-closed state.
claim 3 features the check valve specified in claim 1 or 2, wherein the spring is formed integrally into the valve disc.
With such a configuration that the spring is integrated into the valve disc, it is possible to even more securely suppress axial shift from occurring between the spring and the valve disc, thus maintaining good sealing performance in the valve-closed state.
claim 4 features the check valve specified in claim 1, 2, or 3, wherein the valve disc is mounted at its tip in the valve-closed direction with a sealing member having larger elasticity than the valve disc.
With this configuration, even in such a state where, for example, a shocking valve-closing operation occurs repeatedly to the valve disc, good sealing performance can be maintained when the valve is closed. That is, in such a configuration that, during the above-mentioned valve-closing operation, the valve disc made of a synthetic resin would be directly touched to and separated from the valve seat of the check valve main body, a local portion of the valve disc pressed against the valve seat is liable to have a recess or any other plastic deformation, thus deteriorating sealing performance. To guard against this, as mentioned above, the valve disc is mounted with a highly elastic sealing member in such a configuration that it may be touched to and separated from the valve seat, in order to suppress the above-mentioned plastic deformation at the local portion, thus maintaining good sealing performance in the valve-closed state.
claim 5 features the check valve specified in any one of claims 1 through 4, wherein the check valve main body is divided along the channel in formation into an upstream side main body and a downstream side main body in such a configuration that a lip sealing portion is provided at the positions of these two main bodies facing each other in the channel direction.
Thus, the check valve main body consisting of the upstream-side and downstream-side main bodies has a sealing construction by use of the lip sealing portion to which a sufficient surface pressure is applied, thus suppressing liquid leakage etc. even more securely.
claim 6 features the check valve specified in any one of claims 1 through 5, wherein the check valve main body is divided along the channel in formation into an upstream-side main body and a downstream-side one in such a configuration that outer peripheries of surfaces are welded and sealed, of these two main bodies facing each other in the channel direction.
Thus, with such a sealing construction that the upstream-side and downstream-side main bodies are welded to each other, it is possible to provide a check valve with even improved performance for preventing liquid-leakage etc.
claim 7 features the check valve specified in any one of claims 1 through 6, wherein the above-mentioned synthetic resin is a fluororesin.
With this, it is possible to provide a check valve excellent in corrosion resistance and wear resistance at the same time as being free of metal elution even in the case of flowing of a corrosive fluid.